The present invention relates in general to the timing control of fuel injection in a diesel engine using engine lubrication oil. More particularly the present invention relates to the use of a hydromechanical control valve in combination with a pressure divider as part of a viscosity sensitive auxiliary circuit to provide favorable (improved) performance of an advanced fuel injection timing system.
It has long been known to use engine lubrication oil to advance or retard the timing of fuel injection in a diesel engine. Although normal timing is ideal for a range of engine connected operating conditions, it results in incomplete combustion during idle and low engine speeds because of insufficient pressure in the combustion chamber. Incomplete combustion results in high hydrocarbon emissions and low fuel economy, problems that can be alleviated by injecting fuel into the combustion cylinders sooner.
In the fuel injector shown in FIG. 1 (prior art), advanced timing is achieved by introducing timing fluid into a timing chamber 17, thereby producing a height of fluid which lengthens the link between rocker arm 7 and injector plunger 13. As a result of this lengthened linkage, injector plunger 13 reaches its bottom-most position at an earlier point in the rotation of cam shaft 1. Accordingly, fuel injection occurs at a point in the combustion cycle when the piston of the engine is still moving upward, and while the combustion chamber size is still decreasing. This advancement of injection produces combustion at higher pressures than normal timing because during normal timing injection occurs at a point close to the top dead center position of the piston, and most combustion takes place while the piston is moving downward to increase the combustion chamber size.
Whether and how much timing fluid will be supplied to the timing chamber 17 of the tappet is a function of the pressure of the timing fluid. When the pressure of the timing fluid supply is insufficient to overcome the closure force of check valve 18 in passageway 19, no timing fluid is admitted to chamber 17. Furthermore, the extent to which the pressure of the timing fluid supply exceeds that necessary to open the check valve 18 determines how much timing fluid will actually enter chamber 17. Thus, because timing chamber 17 can be filled during only a limited portion of the cycle of cam shaft 1, if adequate supply pressure is not maintained, even if check valve 18 opens, a proper timing advance will not be obtained. However, due to temperature effects upon the viscosity of the timing fluid, especially the lubricant normally used as a timing fluid, sufficient pressure to properly fill the time control tappets has been very difficult to achieve under all operating conditions. The injector which is illustrated in FIG. 1 is disclosed in U.S. Pat. No. 4,249,499 which issued on Feb. 10, 1981 to Perr.
In order to address some of the concerns expressed herein, work has been done on a flow controlling system having a viscosity sensitive arrangement for producing a simulated fluid pressure. A representative illustration of such work is contained in FIG. 2 (prior art). This simulated pressure varies in correspondence with a fluid pressure at a predetermined portion of a fluid flow circuit on the basis of the viscosity of the fluid flowing through the circuit. The flow controlling system includes a pressure regulating means, that is responsive to changes in the simulated pressure, for maintaining a predetermined pressure at that predetermined portion of the fluid flow circuit. The details of the FIG. 2 prior art illustration are set forth in U.S. Pat. No. 5,024,200 which issued on Jun. 18, 1991 to Free, et al. U.S. Pat. No. 5,024,200 is hereby expressly incorporated by reference for its general background and description of the FIG. 2 system.
The flow controlling system of FIG. 2 is utilized in an engine timing control tappet system of the type having at least one expansible tappet for controlling timing of a fuel injector using oil that is supplied by a pump to an engine lubrication circuit.
One of the concerns of the FIG. 2 arrangement which is to be noted is its performance at warm oil conditions. Although it is desired to maintain or retain the original switch point during warm oil operation, the FIG. 2 arrangement and in particular the systems disclosed in U.S. Pat. No. 5,024,200 have the "penalty" of an increased switch point under warm oil conditions.
In the FIG. 2 arrangement, control valve 28 determines whether or not oil from the engine lubrication circuit is allowed to flow to check valve 18 in FIG. 1. A simplified schematic illustration of the flow logic associated with the valve 28 in U.S. Pat. No. 5,204,200 is provided by FIG. 3 (prior art). A schematic illustration of the hydromechanical control valve 28 which is arranged as a spool valve is provided by FIG. 4 (prior art).
Comparing the present invention to the referenced U.S. Pat. No. 5,024,200, the main improvement is the addition of a temperature sensitive alteration of the injection timing logic. While U.S. Pat. No. 5,024,200 described the use of a viscosity sensitive feature in connection with the supply oil pressure, the present invention introduces a pressure divider which adds a viscosity sensing function to the injection timing decision of the control valve (valve 28). In order to help explain aspects of the injection timing logic based on the present invention, FIGS. 8 and 9 are provided. FIG. 8 shows the switch point between advance and retard as a function of engine oil temperature and FIG. 9 shows the resulting engine operational envelope for injection timing control, depicting the difference between temperature extremes.
In addition to U.S. Pat. No. 5,024,200 which issued Jun. 18, 1991 to Free, et al., there are several other patents which have issued over the years relating to oil viscosity measuring and timing control systems and devices. The following patent references are believed to be representative of these earlier systems and devices:
______________________________________ U.S. Pat. No. Patentee Date Issued ______________________________________ 4,249,499 Perr Feb. 10, 1981 1,863,090 Albersheim et al. June 14, 1932 2,050,242 Booth Aug. 11, 1936 2,194,605 Mapel Mar. 26, 1940 2,035,951 Eckstein Mar. 31, 1936 3,938,369 de Bok Feb. 17, 1976 2,051,026 Booth Aug. 18, 1936 3,204,623 Isley et al. Sept. 7, 1965 3,170,503 Isley et al. Feb. 23, 1965 4,493,302 Kawamura Jan. 15, 1985 4,889,092 Bostwick Dec. 26, 1989 5,181,494 Ausman et al. Jan. 26, 1993 ______________________________________